Why doesn't choosing different object change Shading nodes?
You have pinned you node tree, that means that shader tree is always displayed for that editor regardless of 3D View selection.

Unpin it from the Shader Editor header by clicking the pin icon.
This is useful when comparing materials, if two Node Editors are open, or to make sure you are editing a certain material regardless of selection, like say editing a particle material when the emitter is selected, or editing the material when an collection instance is selected.